| ns-hooks {base} | R Documentation |
Packages with name spaces can supply functions to be called when loaded, attached or unloaded.
.onLoad(libname, pkgname) .onAttach(libname, pkgname) .onUnload(libpath)
libname |
a character string giving the library directory where the package defining the namespace was found. |
pkgname |
a character string giving the name of the package,
including the version number if the package was installed with
--with-package-versions. |
libpath |
a character string giving the complete path to the package. |
These functions apply only to packages with name spaces.
After loading, loadNamespace looks for a hook function named
.onLoad and runs it before sealing the namespace and processing
exports.
If a name space is unloaded (via unloadNamespace),
a hook function .onUnload is run before final unloading.
Note that the code in .onLoad and .onUnload is run
without the package being on the search path, but (unless circumvented)
lexical scope will make objects in the namespace and its imports
visible. (Do not use the double colon operator in .onLoad as
exports have not been processed at the point it is run.)
When the package is attached (via library), the hook
function .onAttach is looked for and if found is called
after the exported functions are attached and before the package
environment is sealed. This is less likely to be useful than
.onLoad, which should be seen as the analogue of
.First.lib (which is only used for packages without a
name space).
.onLoad, .onUnload and .onAttach are looked for
as internal variables in the name space and should not be exported.
If a function .Last.lib is visible in the package, it
will be called when the package is detached: this does need to be exported.
Anything needed for the functioning of the name space should be
handled at load/unload times by the .onLoad and
.onUnload hooks. For example, shared libraries can be loaded
(unless done by a useDynib directive in the NAMESPACE
file) and initialized in .onLoad and unloaded in
.onUnload. Use .onAttach only for actions that are
needed only when the package becomes visible to the user, for example
a start-up message.
If a package was installed with --with-package-versions, the
pkgname supplied will be something like tree_1.0-16.
setHook shows how users can set hooks on the same events.